The effect of fat saturation and level on chemically induced and spontaneous tumors will be studied in mice. the effect of diets high in saturated, monounsaturated, or polyunsaturated fats, ingested at two different fat levels, on initiation and promotion in a two stage skin carcinogenesis system will be evaluated. Beta-propiolactone and dimethylbenzanthracene will be used as initiators and phorbol ester as a promotor. The effect of these diets on spontaneous tumor formation in C3H, AKR, and C3HeB/De mice will also be studied. Skin samples will be obtained for evaluation of lipid peroxidation and for study of mutagenesis using a bacterial system. In addition the possible interaction of dietary fat saturation on microsomal activation of carcinogens will be indirectly assessed.